The present invention relates to Radio Frequency (RF) switches. More specifically, it relates to switching operations of low-loss transistor-based RF switches for high-power RF signals.
RF switches are used to switch between various input signals received by an RF switching circuit and provide the required input signal as its output signal. Further, RF switches may be connected in a series or in a parallel configuration with other circuit elements of the RF switching circuit. RF switches are generally implemented using transistors such as Bipolar Junction Transistors (BJTs), Field Effect Transistors (FETs) and the like. Examples of FETs include Junction Field Effect Transistors (JFETs), Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), Metal Semiconductor Field Effect transistors (MESFETs), pseudomorphic High Electron Mobility Transistors (pHEMTs) and the like. Further, FETs may operate in an enhancement mode or a depletion mode and they may be implemented using n-channel or p-channel semiconductors.
The operation of an FET is controlled using a gate-to-source voltage (Vgs) a drain-to-source voltage (Vds) and a threshold voltage (Vth). In an n-channel depletion-mode FET, the Vth is the voltage at which the n-channel is pinched-off, i.e. the n-channel is depleted of charge carriers and the FET operates in a cut-off mode. In the cut-off mode, the source-to-drain current approaches zero and the FET functions in an off-state. However, when the n-channel is not pinched-off, the FET operates in a triode (linear) mode. In the triode mode, the source-to-drain current is controlled by Vds and the FET functions in an on-state.
RF switches are further classified based on the number of poles and the number of throws for example multi-throw RF switches include Single Pole Double Throw (SPDT) switches, Double Pole Double Throw (DPDT) switches and the like.
RF switches provide one of the received input signals at its output and are controlled using control voltages. Therefore, in an RF switch, only the transistor coupled to the input signal is required to conduct while the remaining transistors are required to be switched-off. Further, the on-transistors may be required to conduct a high-power input RF signal. A high-power RF input signal is a signal for which the corresponding RF peak voltage is high enough to change state of the RF switch by modifying the control voltages. The high-power input RF signal is capable of overriding control voltages that are applied to the off-transistors for maintaining them in the off-state. Therefore, the high-power input RF signal may bias the off-transistors such that they are switched back to the on-state. Hence, an RF signal swing, from a positive excursion to a negative excursion or vice-versa, may switch on the off-transistors. This results in power losses and distortion in the output of the RF switch. Further, resistance of the on-transistors results in conduction losses in the on-state. Therefore, distortion and losses, such as conduction losses and power losses, may occur in both the on-transistors and the off-transistors.
In light of the above, there is a need for a system that provides a bias voltage to the off-transistors for preventing the off-transistors from switching on from the off-state. Hence, the system should reduce the conduction capability of the off-transistors during the signal swing of a high-power input RF signal. Further, there is a need for a system that provides a bias voltage to the on-transistors for reducing their resistance in the on-state. The system should also preferably increase the conduction capability of the on-transistors. Moreover, the system should reduce power losses, conduction losses and distortion that may occur in an RF switch.